Powder metallurgy method

ABSTRACT

Disclosed is a method of manufacturing a molded body. The method may include preparing a liquid or fluid lubricant by admixing an amount of about 50 to 80 parts by weight of ethylene bis stearamide, an amount of about 10 to 30 parts by weight of erucamide, and an amount of about 10 to 50 parts by weight of ester acid at a temperature of about 150 to 170° C., preparing a solid lubricant by cooling the liquid or fluid lubricant to a temperature of about 10 to 30° C., preparing a powder lubricant by pulverizing the solid lubricant to a particle size of about 10 to 75 μm, preparing a powder composition by mixing an amount of about 100 parts by weight of a metal powder and an amount of about 0.5 to 0.8 parts by weight of the powder lubricant, and manufacturing a molded body using the powder composition, wherein all the parts by weight are based on the 100 parts by weight of the metal powder.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims, under 35 U.S.C. § 119(a), the benefit of priority to Korean Patent Application No. 10-2018-0052602, filed May 8, 2018, the entire contents of which is incorporated herein for all purposes by reference.

TECHNICAL FIELD

The present invention relates to a method of manufacturing a molded body using a metal composition. The method can provide the molded body including a powder lubricant thereby increasing density of the molded body.

BACKGROUND OF THE INVENTION

As power of engines increases, engines and transmission parts of vehicles require improved mechanical properties. Various molding technologies have been developed for improving the mechanical properties, but there is a limit in application of the molding technologies due to the increase in manufacturing cost of the parts and the breakage of molds in the high-pressure molding. Accordingly, in the related arts, a lubricant has been included in the molding to maintain a high density at a pressure (for example, 400 to 700 MPa) as applied in conventional molding.

In the related arts, lubricants have been used for the purpose of reducing the internal friction between metal-based powder particles during a molding and compression process, securing uniform compression in the powder metallurgy, and minimizing damage to a die. However, when the metal-based powder containing the lubricant is extrusion-molded, the lubricant may remain between the metal-based powder particles, so that a high-density molded body may not be obtained. However, when the amount of the lubricant added to the metal-based powder is reduced, the frictional resistance may be increased between a green compact and the wall surface of a mold. Accordingly, since demolding force is increased when the green compact is withdrawn from the mold, damage to the mold, such as wear of the mold, may occur. Further, during rearrangement of the metal-based powder particles, which may occur upon compression-molding, the lubricity between the powder particles may be reduced, so improvement of the density of the green compact may not be obtained. For instance, in the related arts, as the lubricant for high-density molding, amide-based wax containing ethylene bis stearamide (EBS) has been generally used.

Moreover, in the related arts, mechanical mixing method of performing simple mixing and a polymerization method of polymerizing a monomer including a lubricant base material have been used. The mechanical mixing method may include crushing the lubricant base material to a size of 25 μm or less and then adding the metal-based powder and the lubricant base material to a mixer with mixing. Accordingly, the mechanical mixing method may have a merit in that the process is relatively simple, however, the addition amount of the lubricant may not be reduced because of the high ejection energy and low surface roughness of the molded body may not be obtained .

The method of manufacturing the lubricant using the polymerization reaction may provide a merit in that homogeneity and low ejection energy are secured because chemical bonding may be induced between the molecules of lubricant base materials, however, that process costs are greatly increased due to the complicated process.

SUMMARY OF THE INVENTION

In preferred aspects, the present invention provides a method of manufacturing a molded body which may include a small amount of powder lubricant. The molded body may have increased density t.

In one aspect, the present invention provides a method including: preparing a liquid or fluid lubricant by admixing an amount of about 50 to 80 parts by weight of ethylene bis stearamide, an amount of about 10 to 30 parts by weight of erucamide, and an amount of about 10 to 50 parts by weight of ester acid; preparing a solid lubricant by cooling the liquid or fluid lubricant; preparing a powder lubricant by pulverizing the solid lubricant; preparing a powder composition by mixing an amount of about 100 parts by weight of a metal powder and an amount of about 0.5 to 0.8 parts by weight of the powder lubricant, and forming the molded body using the powder composition, wherein all the parts by weight herein are based on the 100 parts by weight of the metal powder.

The term “liquid or fluid” as used herein refers to a material or substance, or a property thereof that change shape or direction uniformly in response to an external force or in accordance to a shape of a container. The term “liquid or fluid lubricant” as used herein refers to a material having lubricant proprieties, for example, reduce friction between surfaces in contact, by including liquid or fluid.

The term “ethylene bis stearamide” as used herein refers to a compound including two stearamide groups (e.g., two amide groups each attached to substituted or unsubstituted C₁₇ alkyl) and linked by ethylene (e.g., saturated or unsaturated, and substituted or unsubstituted alkylene such as —(CH₂)₂—). Preferred ethylene bis stearamide compound may have the following structure,

The term “erucamide”, “erucilamide” or a “erucyl amide” as used herein refers to a compound including an amide group attached to one or more alkyl or alkylene (e.g., C₂₁ alkyl or alkylene) which may be substituted or unsubstituted. Preferred erucamide may have the formula of CH₃(CH₂)₇CH═CH(CH₂)₁₁COOH. In certain preferred embodiments, the erucamide may be Z (cis) form compound having the formula of CH₃(CH₂)₇CH═CH(CH₂)₁₁COOH.

The term “ester acid” as used herein refers to a compound including one or more ester

attached to one or more of alkyl or alkylene (e.g., C₂-C₄₀ alkyl or alkylene) which may be substituted or unsubstituted. Preferred ester acid may further include one or more hydroxy group, ketone, fatty acid or alcohol. In certain preferred embodiments, the ester acid may not include hydroxy group, ketone, fatty acid or alcohol.

The ester acid may suitably include at least one or more selected from montan wax, glycerol monostearate, glycerol monooleate, and distearyl phthalate. The liquid or fluid lubricant may be prepared by mixing and agitating for about 10 to 30 minutes. The liquid or fluid lubricant may be prepared by mixing and agitating for at a temperature of about 150 to 170° C.

The liquid or fluid lubricant may be cooled to a temperature of about 10 to 30° C.

The powder lubricant may have a particle size of about 10 to 75 μm.

The molded body may be suitably formed by applying a pressure to the power composition. Preferably, the pressure may be of about 500 to 700 MPa.

The molded body may be suitably formed manufactured by applying an ejection force of about 800 to 1,100 kgf to thus eject the molded body from a mold.

Preferably, the molded body may have a density of about 7.2 to 7.3 g/cm³.

In another aspect, provided is a molded body manufactured by the method as described herein.

Still further provided is a vehicle including the molded body as described herein.

According to the preferred method according to various exemplary embodiments of the present invention, a molded body, for example, a molded body for a vehicle, having increased density may be produced using same ejection energy in the related arts by adding a small amount of powder lubricant.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flowchart schematically showing an exemplary method of manufacturing a molded body according to an exemplary embodiment of the present invention;.

FIGS. 2A, 2B, 2C, 2D, 2E, 2F, 2G, and 2H are, respectively, graphs obtained by measuring ejection forces in Examples 1 to 8 according to exemplary embodiments of the present invention.

FIG. 3A is a graph obtained by measuring ejection forces in Comparative Example 1 and in cases the same as Comparative Example 1 with the exception that the composition of ethylene bis stearamide and erucamide is changed. Comparative Example 1 corresponds to #4 of FIG. 3A, and #3, #2, and #1 are the same as Comparative Example 1 except that the composition of ethylene bis stearamide and erucamide is changed to 60:40, 55:45, and 50:50, respectively.

FIG. 3B is a graph obtained by measuring ejection force in Comparative Example 2, which shows the results of Comparative Example 2 tested three times for #1, #2, and #3.

DETAILED DESCRIPTION

The above and other aspects, features and advantages of the present invention will be more clearly understood from the following preferred embodiments taken in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed herein, but may be modified into different forms. These embodiments are provided to thoroughly explain the invention and to sufficiently transfer the spirit of the present invention to those skilled in the art.

Throughout the drawings, the same reference numerals will refer to the same or like elements. For the sake of clarity of the present invention, the dimensions of structures are depicted as being larger than the actual sizes thereof. It will be understood that, although terms such as “first”, “second”, etc. may be used herein to describe various elements, these elements are not to be limited by these terms. These terms are only used to distinguish one element from another element. For instance, a “first” element discussed below could be termed a “second” element without departing from the scope of the present invention. Similarly, the “second” element could also be termed a “first” element. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise.

It will be further understood that the terms “comprise”, “include”, “have”, etc. when used in this specification specify the presence of stated features, integers, steps, operations, elements, components, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof. Also, it will be understood that when an element such as a layer, film, area, or sheet is referred to as being “on” another element, it can be directly on the other element, or intervening elements may be present therebetween. In contrast, when an element such as a layer, film, area, or sheet is referred to as being “under” another element, it can be directly under the other element, or intervening elements may be present therebetween.

It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g. fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles.

Further, unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. “About” can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about.”

Hereinafter, preferred methods according to an Example in exemplary embodiments of the present invention will be described.

FIG. 1 is a flowchart schematically showing an exemplary method of manufacturing a molded body (“powder metallurgy method”) according to the Example in an exemplary embodiment of the present invention.

As shown in FIG. 1, the powder metallurgy method according to the Example of the present invention may include preparing a liquid or fluid lubricant by admixing (e.g., mixing and agitating) an amount of about 50 to 80 parts by weight of ethylene bis stearamide, an amount of about 10 to 30 parts by weight of erucamide, and an amount of about 10 to 50 parts by weight of ester acid at a temperature of about 150 to 170° C. (S100), preparing a solid lubricant by cooling the lubricant, for example, to a temperature of about 10 to 30° C. (S200), preparing a powder lubricant by pulverizing the solid lubricant, for example, to a particle size of about 10 to 75 μm (S300), preparing a powder metallurgy composition by mixing an amount of about 100 parts by weight of a metal powder and an amount of about 0.5 to 0.8 parts by weight of the powder lubricant (S400), and forming a molded body, for example, by applying a pressure or compression-molding the powder composition (S500). All the parts by weight are based on the 100 parts by weight of the metal powder.

In an exemplary embodiment, an amount of about 50 to 80 parts by weight of the ethylene bis stearamide, an amount of about 10 to 30 parts by weight of the erucamide, and an amount of about 10 to 50 parts by weight of the ester acid may be mixed and agitated at a temperature of about 150 to 170° C., thus manufacturing the liquid or fluid lubricant (S100).

Preferably, an amount of about 50 to 80 parts by weight of the ethylene bis stearamide, an amount of about 10 to 30 parts by weight of the erucamide, and an amount of about 10 to 50 parts by weight of the ester acid may be mixed based on the liquid or fluid lubricant. When the powder lubricant is formed using the liquid or fluid lubricant manufactured in the above-described range, high density of the molded productmay be obtained, and the ejection energy may be reduced while minimizing the amount of the powder lubricant that is added when mixing with the metal powder.

The ester acid may include one or more selected from montan wax, glycerol monostearate, glycerol monooleate, and distearyl phthalate.

The step of manufacturing the liquid or fluid lubricant (S100) may be performed, for example, by providing the ethylene bis stearamide, the erucamide, and the ester acid to a chamber (e.g., reaction chamber) and heating the chamber.

When the step of manufacturing the liquid or fluid lubricant (S100) is performed at a temperature less than 150° C., since the ethylene bis stearamide and the erucamide are not evenly distributed, there may be a limit in reduction of the ejection energy, and a molded body having high surface roughness (Ra) may be manufactured. When the step of manufacturing the liquid or fluid lubricant (S100) is performed at a temperature greater than about 170° C., oxidation of the erucamide having a low melting point may occur, and discoloration and an increase in viscosity of the erucamide may occur, which may be drawbacks in crushing.

The step of manufacturing the lubricant (S100) may suitably be performed for about 10 to 30 minutes. When the step of manufacturing the lubricant (S100) is performed for less than 10 minutes, the time may be short to perform sufficient melting and polymerization of various components. When the step of manufacturing the lubricant is performed for more than 30 minutes, a substance having a low melting point may be volatilized first.

The liquid or fluid lubricant may be cooled to a temperature of about 10 to 30° C. to thus manufacture the solid lubricant (S200). In the step of cooling the liquid or fluid lubricant to thus manufacture the solid lubricant (S200), the liquid or fluid lubricant may be cooled to thus form, for example, a cake-type solid lubricant. When the step of cooling the lubricant to thus manufacture the solid lubricant (S200) is performed at a temperature greater than about 30° C., excessive cooling time may be required.

The solid lubricant may suitably be pulverized to a particle size of about 10 to 75 μm to thus manufacture the solid powder lubricant (S300). When the particle size of the solid powder lubricant is less than about 10 μm or is greater than about 75 μm, during mixing with the metal powder, uniform mixing may not be secured.

Preferably, an amount of about 100 parts by weight of the metal powder and an amount of about 0.5 to 0.8 parts by weight of the powder lubricant may be suitably admixed or mixed to thus manufacture the powder metallurgy composition (S400). The powder lubricant may realize lubricity between the metal powder and the mold and between the metal powders when the molded body is manufactured. When the amount of the powder lubricant is less than an amount of about 0.5 parts by weight, the ejection force of the molded body may be reduced. When the amount of the powder lubricant is greater than about 0.8 parts by weight, the density of the molded body may be reduced.

The powder metallurgy composition may be compression-molded to thus manufacture the molded body (S500). The step of manufacturing the molding body (S500) may include compression at a pressure of about 500 to 700 MPa. When the compression is performed at the pressure less than about 500 MPa, the molded body may not be sufficiently compressed. When the compression is performed at the pressure greater than about 700 MPa, fine cracks may be formed in the molded body, which may cause a problem of low durability.

The step of manufacturing the molded body (S500) may include applying an ejection force of about 800 to 1,100 kgf to thus eject the molded body from the mold. In the case where the ejection force is out of the above-mentioned range, when the ejection force is less than about 800 kgf, the density of the molded body may be reduced due to the excessive amount of the lubricant. When the ejection force is greater than about 1,100 kgf, the inner wall of the mold may be damaged.

The step of manufacturing the molded body (S500) may include manufacturing the molded body having a density of about 7.2 to 7.3 g/cm³. When the density is less than about 7.2 g/cm³, the durability of the molded body may be reduced due to the low density. When the density is about 7.3 g/cm³ or greater, since the friction force with the mold is increased due to the excessive pressure, the ejection force may be reduced.

In the powder metallurgy method according to exemplary embodiments of the present invention, a small amount of powder lubricant may be added to thus manufacture a molded body having increased density while securing the same ejection energy as in the related art. In particular, the effect of increasing the density by about 0.15 g/cm³ may be secured, compared to the molded body manufactured by adding the powder lubricant manufactured using conventional mechanical mixing and polymerization methods.

Hereinafter, the present invention will be described more specifically with reference to specific Examples. The following Examples are provided to aid understanding of the present invention, and the scope of the present invention is not limited thereto.

EXAMPLES Example 1

Ethylene bis stearamide, erucamide, and glycerol monostearate (ester acid) were mixed at a ratio of the parts by weight shown in the following Table 1, and were agitated at a temperature of 160° C. for 20 minutes to thus manufacture a liquid lubricant. The liquid lubricant was cooled to a temperature of 20° C. to thus manufacture a cake-type solid lubricant. The resultant lubricant was pulverized to a particle size of 10 to 75 μm to thus manufacture a solid powder lubricant.

As a metal powder, HSPP (Hyundai Steel, Pure iron Powder) was prepared. 100 parts by weight of the metal powder and 0.8 parts by weight of the solid powder lubricant were mixed to thus manufacture a powder metallurgy composition. The powder metallurgy composition was placed in a die, and a molding pressure of 500 MPa was applied to thus manufacture a molded body.

Example 2

The same procedure as in Example 1 was performed except that 0.5 parts by weight of the solid powder lubricant was mixed therein to thus manufacture the powder metallurgy composition.

Example 3

The same procedure as in Example 1 was performed except that mixing was performed at a ratio of the parts by weight shown in the following Table 1.

Example 4

The same procedure as in Example 3 was performed except that 0.5 parts by weight of the solid powder lubricant was mixed therein to thus manufacture the powder metallurgy composition.

Example 5

The same procedure as in Example 1 was performed except that mixing was performed at a ratio of the parts by weight shown in the following Table 1.

Example 6

The same procedure as in Example 5 was performed except that 0.5 parts by weight of the solid powder lubricant was mixed therein to thus manufacture the powder metallurgy composition.

Example 7

The same procedure as in Example 1 was performed except that mixing was performed at a ratio of the parts by weight shown in the following Table 1.

Example 8

The same procedure as in Example 7 was performed except that 0.5 parts by weight of the solid powder lubricant was mixed therein to thus manufacture the powder metallurgy composition.

Comparative Example 1

Ethylene bis stearamide and erucamide were prepared. They were mixed at a ratio of the parts by weight shown in the following Table 1, and were agitated at a temperature of 160° C. for 20 minutes to thus manufacture a liquid lubricant. The liquid lubricant was cooled to a temperature of 20° C. to thus manufacture a cake-type solid lubricant. The resultant lubricant was pulverized to a particle size of 10 to 75 μm to thus manufacture a solid powder lubricant.

As a metal powder, HSPP (Hyundai Steel, Pure iron Powder) was prepared. 100 parts by weight of the metal powder and 0.8 parts by weight of the solid powder lubricant were mixed to thus manufacture a powder metallurgy composition. The powder metallurgy composition was placed in a die, and a molding pressure of 500 MPa was applied to thus manufacture a molded body.

Comparative Example 2

The same procedure as in Comparative Example 1 was performed, except that a conventional polymerization method was used when the liquid lubricant was manufactured.

TABLE 1 Lubricant Addition Manufacturing Constitution amount (parts method of No. (parts by weight) by weight) lubricant Example 1 EBS:erucamide:glycerol 0.8 160° C. Example 2 monostearate (60:10:30) 0.5 Example 3 EBS:erucamide:glycerol 0.8 160° C. Example 4 monostearate (50:10:40) 0.5 Example 5 EBS:erucamide:glycerol 0.8 160° C. Example 6 monostearate (70:10:20) 0.5 Example 7 EBS:erucamide:glycerol 0.8 160° C. Example 8 monostearate (80:10:10) 0.5 Comparative EBS:erucamide (70:30) 0.8 160° C. Example 1 Comparative 0.8 Polymerization Example 2

Measurement of Physical Properties

Ejection force was measured based on MPIF Standard 45, and is shown in Table 2 below. FIGS. 2A, 2B, 2C, 2D, 2E, 2F, 2G, and 2H show graphs obtained by measuring the ejection forces in Examples 1 to 8. Further, the ejection forces in Comparative Examples 1 and 2 were measured, and are shown in

FIGS. 3A and 3B. Further, the density of the molded body was measured, and is shown in Table 2.

TABLE 2 No. Ejection force (Kgf) Density of molded body (g/cm³) Example 1 850~900 7.20 Example 2 1,000~1,100 7.22 Example 3 800~950 7.25 Example 4   950~1,050 7.30 Example 5   900~1,100 7.20 Example 6   950~1,300 7.23 Example 7 1,100~1,300 7.22 Example 8 1,600~2,000 7.24 Comparative 1,100~1,400 7.12 Example 1 Comparative 1,500 7.10 Example 2

Evaluation of Physical Properties

As shown in Table 2, the density in Example 1 was similar to the density in Comparative Examples 1 and 2, but that the ejection force in Example 1 was relatively less than the ejection force in Comparative Examples 1 and 2.

Although various exemplary embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art will appreciate that the present invention may be embodied in other specific forms without changing the technical spirit or essential features thereof. Thus, the embodiments described above should be understood to be non-limiting and illustrative in every way. 

What is claimed is:
 1. A method of manufacturing a molded body, comprising: preparing a liquid or fluid lubricant by admixing an amount of about 50 to 80 parts by weight of ethylene bis stearamide, an amount of about 10 to 30 parts by weight of erucamide, and an amount of about 10 to 50 parts by weight of ester acid; preparing a solid lubricant by cooling the liquid or fluid lubricant; preparing a powder lubricant by pulverizing the solid lubricant; preparing a powder composition by mixing an amount of about 100 parts by weight of a metal powder and an amount of about 0.5 to 0.8 parts by weight of the powder lubricant; and forming the molded body using the powder composition wherein all the parts by weight based on the 100 parts by weight of the metal powder.
 2. The method of claim 1, wherein the ester acid comprises one or more selected from montan wax, glycerol monostearate, glycerol monooleate, and distearyl phthalate.
 3. The method of claim 1, wherein the liquid or fluid lubricant is prepared by mixing and agitating for about 10 to 30 minutes.
 4. The method of claim 1, wherein the liquid or fluid lubricant is prepared by mixing and agitating for at a temperature of about 150 to 170° C.
 5. The method of claim 1, wherein the liquid or fluid lubricant is cooled to a temperature of about 10 to 30° C.
 6. The method of claim 1, wherein the powder lubricant has a particle size of about 10 to 75 μm.
 7. The method of claim 1, wherein the molded body is formed by applying a pressure to the powder composition.
 8. The method of claim 7, wherein the pressure is of about 500 to 700 MPa.
 9. The method of claim 1, wherein the molded body is formed by applying an ejection force of about 800 to 1,100 kgf to thus eject the molded body from a mold.
 10. The method of claim 1, wherein the molded body has a density of about 7.2 to 7.3 g/cm³.
 11. A molded body manufactured by a method of claim
 1. 12. A vehicle comprising a molded body of claim
 11. 